Abstract: ob＜x＞jective By observing the changes of heart rate variability (HRV) time domain parameters in patients with generalized anxiety disorder (GAD), we try to find reliable physiological quantitative indicators to provide ob＜x＞jective basis for early diagnosis of GAD patients .Methods The beck anxiety inventory (BAI) was used to score the scale for patients who met the clinical diagnosis of GAD. Those with a score ≥ 45 were included in the observation group (56 cases). Meanwhile, for eligible normal population, the score < 45 was included in the control group (52 cases). 24 hours ambulatory electrocardiogram was performed in 108 cases to measure five HRV time domain parameters. pNN50 and rMSSD reflects the function of parasympathetic nerves; SDNN-Index reflects changes in sympathetic tension; SDNN reflects the ability to regulate autonomic nerves overall; and trigonometric index expressed all HRV within 24 hours. Results The observation group, compared with the control group, had lower pNN50 (-4.08%)，rMSSD (-8.65ms) and SDNN-Index (-7.91ms) (P ≤ 0.004). However,SDNN and trigonometric index was not significantly different between the two groups (P ≥ 0.24). Conclusion The patients with GAD showed decreased parasympathetic function and increased sympathetic activity. The HRV time domain parameters, including pNN50, rMSSD and SDNN-Index, can be used as ob＜x＞jective indicators for early GAD diagnosis.